Introduction to Nanoscience What is happening at a very, very small length scale?

Introduction to Nanoscience

What is happening at a very, very small length scale?

Aniruddha ChakrabortySchool of Basic SciencesIndian Institute of Technology Mandi,Mandi, Himachal Pradesh, India.E-mail: achakraborty@iitmandi.ac.inWeb: www.iitmandi.ac.in

Acknowledgements

• Prof. K. L. Sebastian, IISc, Bangalore, India.

• Organizers of NSNT, IIT Mandi, Himachal Pradesh, India.

• Students, ’Nanoscience’ course (CY342).

Plan of the talk• What is Nano scale Science?

• Actual physical dimensions relevant to Nano systems.

• Properties of Nanomaterial.

• Size & Shape Dependent Properties – at Nano scale.

• Conclusions.

• Suggested Readings.

What is Nano ? Nano - a prefix that means very, very, small !

• Question : How small is ‘Nano’ ? Answer: “One billionth" of something, or 0.000000001.

=

‘Nano’ length scale ?

What is Nanometer ?

• A nanometer is one billionth of a meter.

• Nanoscale is actually Nanometer scale. • Nanometer scale range from approximately 100 nm to 1 nm.

Accurate definition of nanometer scale ?

Nanoscience: Nanometer scale

science• A part of science that studies small stuff So, what is Nano science ?• It is not only Biology. • It is not only Physics .• It is not only Chemistry. • It is all sciences that work with the very small.

Nanoscience is not physics, chemistry, engineering or biology. It is all of them.

S.M. Lindsay, Introduction to Nanoscience, Oxford University Press (2009).

0.1nm 1nm 10nm 100nm 1m 10 m

Nanoscience

Size and shape dependent properties

Nanometer scale : The length scale where corresponding property is size & shape dependent.

Actual physical dimensions relevant to

Nanosystem

• Bohr radius = 0.5292Å ≈ 0.05 nm • C atom (VdW radius)=0.17 nm• In a 1nm line: 3C atoms• In a 1nm x 1nm surface: 9C atoms• In a 1nm x 1nm x 1nm cube: 27 C atoms• In a 100 nm x 100 nm x 100 nm cube: 2.7 x 107 C atoms

• In a 1m x 1m x 1m cube: 2.7 x 1028 C atoms

Typical nanosystems may contain from hundreds to tens of thousands of atoms.

Length Scale

Nanosystems: % of Surface atomsExample of Gold Nano particle:

Sphere of radius 12.5 nm contains total approx. 480,000 atoms. surface contains approx. 48,000 atoms.So, approx. 10% atoms are on the surface.

Sphere of radius 5 nm contains total approx. 32,000 atoms. surface contains approx. 8000 atoms.So, approx. 25% atoms are on the surface.

Surface atoms have unused electrons – so very reactive (can be used for catalysis)

• Nano sized particles exhibit different properties than larger particles of the same substance.

• Nano sized particle exhibit size & shape dependent properties.

What’s interesting about the nanoscale?

How do properties change at the Nanoscale ?

Properties of a Material

A property describes how a material acts under certain conditions.• Types of properties:

Optical (e.g. color). Electrical (e.g. conductivity). Physical (e.g. melting point). Chemical (e.g. reaction rate).

• Properties are usually measured by looking at large (~1023) aggregations of atoms or molecules.

Sources: http://www.bc.pitt.edu/prism/prism-logo.gif

http://www.physics.umd.edu/lecdem/outreach/QOTW/pics/k3-06.gif

Optical Properties: Colour of Gold• Bulk gold

appears yellow in colour.

• Nano sized gold appears red in colour.The particles are so small that electrons are not free to move about as in bulk gold Because this movement is restricted, the particles react differently with light.

Sources:

http://www.sharps-jewellers.co.uk/rings/images/bien-hccncsq5.jpg

http://www.foresight.org/Conferences/MNT7/Abstracts/Levi/

12 nanometer gold clusters of particles look red.

Physical Property: Melting Point of a Substance

• Melting Point (microscopic definition)– Temperature at which the atoms, ions, or molecules in a

substance have enough energy to overcome the intermolecular forces that hold the them in a “fixed” position in a solid

– Surface atoms require less energy to move because they are in contact with fewer atoms of the substance.

In contact with 3 atomsIn contact with 7 atoms

http://serc.carleton.edu/usingdata/nasaimages/index4.html

At the macro scale

At the Nanoscale

The majority of the atoms are…

…almost all on the inside of the object

…split between the inside and the surface of the object

Changing an object’s size…

…has a very small effect on the percentage of atoms on the surface

…has a big effect on the percentage of atoms on the surface

The melting point…

…doesn’t depend on size … is lower for smaller particles

Understanding Melting Point: macro vs. nano

Electrical Properties :Conductivity of Nanotubes• Nanotubes are long, thin cylinders of carbon:Their electrical properties change with diameter, “twist”, and number of wallsThey can be either conducting or semi-conduc their electrical behavior.

Chemical Property: Reaction Rate• Nano particles are very small in size.

• Very high surface area to volume ratio.

• Reactions are very quick.

Things are different at different Length Scale

• There are enormous Length scale differences

in our universe!• At different scales Different forces dominate.

Different models better explain phenomena.

Length Scale - Changes Everything Three important ways in which Nanoscale materials may

differ from macro scale materials

1. Gravitational forces become negligible and electromagnetic forces dominate.

2. Quantum mechanics is the model used to describe motion and energy instead of the classical mechanics model.

3. Greater surface to volume ratios.

Dominance of Electromagnetic Forces Gravitational force is a function of mass and distance and is weak between (low-mass) Nano sized particles.

Electromagnetic force is a function of charge and distance is not affected by mass, so it can be very strong even when we have Nano sized particles.

Sources: http://www.physics.hku.hk/~nature/CD/regular_e/lectures/images/chap04/newtonlaw.jpghttp://www.antonine-education.co.uk/Physics_AS/Module_1/Topic_5/em_force.jpg

Quantum Effects

Sources: http://www.phys.ufl.edu/~tschoy/photos/CherryBlossom/CherryBlossom.htmlhttp://www.nbi.dk/~pmhansen/gold_trap.ht; http://www.sharps-jewellers.co.uk/rings/images/bien-hccncsq5.jpg;

Classical mechanical models that we use to understand matter at the macro scale break down for…• The very small (Nanoscale) systems.

Quantum mechanics better describes phenomena that classical physics cannot, like…• The colors of Nano gold• .The probability (instead of certainty) of where an electron will be

found.• Below a certain length scale (that depends on interaction

strengths) systems must be described using quantum mechanics.

Surface to Volume Ratio Increases As surface to volume ratio increases

• A greater amount of a substance comes in contact with surrounding material.

• This results in better catalysts, since a greater proportion of the material is exposed for potential reaction.

Three Generic NanostructuresQuantum Dot 0 Degree Of Freedom 3 dimensional confinement

Quantum Wire 1 Degree Of Freedom 2 dimensional confinement

Quantum Well 2 Degrees of Freedom 1 Dimensional Confinement

Source: http://www.hyperorg.com/blogger/images/sunrise_medium1.jpg

Nano science: A New DayThe Nano science revolution will lead

to… New areas of research . Better understanding of matter and

interactions. New ways to tackle important problems in

science.By learning about an individual atom’s/molecule’s properties, we can put them together in very well-defined ways to produce new materials with new and amazing characteristics.

• Nanoscience refers to the science with dimensions in the range from 1-100 nanometres.

• In Nano science building blocks may consist of anywhere from a few hundred atoms to millions of atoms.

• In Nanoscale, properties (electrical, mechanical, optical, chemical, and biological) are fundamentally different from bulk.

• In Nanoscale, properties (electrical, mechanical, optical, chemical, and biological) are shape and size dependent.

Conclusions

Suggested Readings1. Introduction to Nanoscience : S. M. Lindsay, Oxford, 2010.

2. Nanotechnology: Understanding small systems : Rogers, Pennathur & Adams, CRC press, 2008.

3. Introductory Nanoscience : Masaru Kuno, Garland Science, 2011.

4. Quantum Mechanics for Nanostructures : Vladimir V. Mitin, Dimitry I. Sementsov & Nizami Z. Vagidov, Cambridge, 2010.

5. Nanophysics and Nanotechnology: An introduction to the modern concepts in Nanoscience: Edward L. Wolf, Wiley-VCH, 2011.

6. Introductory Quantum Mechanics : Richard L. Liboff, Addison-Wesley, 1993.

7. Foundations of Nano mechanics: A. N. Cleland, Springer, 2003.

This tutorial slides will be available at www.iitmandi.academia.edu/AniruddhaChakraborty

Thank You !